The present invention relates to a method and apparatus for isolating a fuel cell assembly from its surroundings, such as for protection against dehydration during shutdown or for other purposes, such as protection against contaminants.
Electrochemical fuel cells convert reactants, namely, fuel and oxidant, into reaction products and in the process generate electric power. In a typical fuel cell using hydrogen gas as fuel and oxygen or compressed air as oxidant, the reaction product is water.
Solid polymer fuel cells typically employ a membrane electrode assembly (MEA) comprising a solid polymer electrolyte or ion exchange membrane disposed between two electrode layers. The membrane, in addition to being an ion conductive (typically proton conductive) material, also acts as a barrier for isolating the reactant fluid streams from each other. The MEA is interposed between two electrically conductive separator plates impermeable to the reactant flow streams and having flow channels forming flow fields to direct the fuel and oxidant to the respective electrode layers.
In a fuel cell stack, a plurality of fuel cells are connected together to increase the overall output power of the assembly. The fuel cell stack is interposed between a pair of end plates have inlet and outlet ports associated therewith for feeding and exhausting the oxidant and fuel fluid streams, respectively. The end plates may also have inlet and outlet ports associated therewith for flowing a coolant stream through the stack.
It is desirable that the ion-exchange membrane in the fuel cell stack be kept moist to maintain adequate ionic conductivity and to reduce structural damage that may result if the membranes are allowed to become too dry. It is known that leaks in membranes may occur near reactant stream inlet ports. Such leaks may be caused or worsened by membrane dehydration during fuel cell stack operation, thereby resulting in the formation of cracks or holes.
In a phosphoric acid electrolyte fuel cell stack, it is desirable to prevent water from entering the stack during shutdown periods. Additionally, it is desirable in some applications to protect the fuel cell stack from contaminants or other hazards, such as exposure to salt water, particularly in marine applications.
An improved method isolates an electrochemical fuel cell assembly from its surroundings, the fuel cell assembly having an access opening formed therein. The access opening is either of a reactant stream inlet port or a reactant stream outlet port for directing a working fluid stream (such as, for example, a coolant stream) to or from the fuel cell stack or other component in the fuel cell assembly (for example, a reactant stream humidifier). In a preferred embodiment, the access opening is an opening formed in an enclosure containing the fuel cell assembly. The improved method comprises the steps of:
(a) providing the access opening with a closure member that is normally biased to a closed position in which the access opening is closed, the closure member having a pressure activated actuator for urging the closure member to an open position when the actuator is exposed to pressure; and
(b) operatively connecting the actuator to a fluid stream of the fuel cell assembly such that the actuator is exposed to fluid pressure of the fluid stream for urging the closure member to the open position, thereby opening the access opening.
In preferred embodiments, the access opening is an oxidant stream inlet or an oxidant stream outlet, and the fluid stream that provides the actuating pressure is a fuel stream.
An improved fuel cell assembly has an access opening formed therein through which the assembly is exposed to its surroundings. The improved assembly comprises a closure member that is movable between an open position and a closed position, the closure member being operatively associated with the access opening and normally biased to the closed position such that when the access opening is closed the fuel cell assembly is isolated from its surroundings. In operation, the closure member preferably includes a pressure-activated actuator for urging the closure member to the open position when the actuator is exposed to pressure. The actuator optionally comprises a conduit fluidly connected to a fluid stream of the fuel cell assembly for exposing the actuator to the fluid stream pressure and urging the closure member to the open position, thereby opening the access opening.
An improved fuel cell assembly also comprises a solid polymer electrolyte fuel cell comprising first and second fluid flow channels and an isolation valve that is switchable between a closed position and an open position for, respectively, closing and opening said first fluid flow channel. The valve is normally biased to the closed position for closing the first fluid flow channel during shutdown of the fuel cell assembly. The valve further includes an actuator that is responsive to fluid pressure in the second fluid flow channel during start up of the fuel cell assembly for switching the valve to the open position.